In a semiconductor manufacturing process, in order to fill holes between wirings formed on a semiconductor wafer as a substrate to be processed (hereinafter, referred to as a “wafer”), or in order to provide a barrier layer, a thin film is formed by depositing a metal such as Ti, Al, Cu or the like or a metal compound such as WSi, TiN, TiSi or the like. Such thin film of the metal or metal compound is formed by means of a CVD method which has a better buriability compared to a physical vapor deposition (PVD) method.
A CVD film forming apparatus includes: a wafer stage provided in a chamber and having a heater embedded therein; and a shower head, provided above and opposite to the stage, for injecting a processing gas. A processing space in the chamber is set to a predetermined vacuum level. A wafer on the stage is heated to a predetermined temperature, while the processing gas is continuously supplied from the shower head into the chamber. Accordingly, a chemical reaction occurs on a wafer surface, and a reaction product is deposited on the wafer surface. As a consequence, a film is formed.
When a TiN film is formed on a wafer by using, e.g., TiCl4 and NH3, as processing gases, a portion of the shower head which comes into contact with the processing space needs to be temperature controlled in order to prevent adhesion of a lower-order of TiClx generated from the processing gases to the wafer. Therefore, a heater may be provided on the side of the shower head.
Meanwhile, in order to form a high-quality thin film while ensuring excellent adhesivity and step coverage, a film forming process may be performed by using a technique referred to as “SFD” (sequential flow deposition) which is one of the CVD methods. The SFD is a method for forming a thin film having a desired thickness by laminating a molecular layer on a wafer by repeating cycles of supplying a processing gas containing a film forming material into the processing space of the chamber intermittently.
When the film forming process is performed by the SFD, energy needs to be supplied to the processing gas in a short period of time in order to facilitate intermittent chemical reaction. Therefore, compared to the conventional CVD, a temperature of the heater provided at the stage is set to a higher level.
However, when the temperature of the heater of the stage increases, a temperature of a shower head surface which comes in contact with the processing space increases by heat radiated from the heater of the stage during the film forming process. As a result, a film of the processing gas is easily formed on the shower head surface.
In that state, if the film is adhered to the shower head, the film absorbs heat and, thus, the temperature of the shower head increases further. Moreover, due to the temperature increase, the film is more easily adhered to the shower head, and the temperature of the shower head increases even further, leading to a vicious cycle. As a result, it is not possible to perform the temperature control by the heater provided on the side of the shower head. That is, the temperature control of the shower head which is required in the film forming process may not be performed. Further, when the shower head is made of nickel, if the temperature of the shower head cannot be controlled and thus is beyond a tolerance range, a nickel compound is generated in the shower head, which may cause generation of particles.
Here, Japanese Patent Laid-open Application No. 2002-327274 (particularly, paragraph [0038], FIG. 1) describes a film forming apparatus including a heating unit provided above a shower head and a cooling unit provided above the heating unit. However, in the above-described cooling unit, when the temperature control is required for suppressing a temperature increase of the shower head due to heat from a processing space as in the SFD, the cooling operation is applied from above the heating unit without being directly applied to the shower head, thus deteriorating the cooling responsiveness. That is, the temperature of the shower head surface facing the processing space cannot be controlled with high accuracy.